Polishing composition and use thereof

ABSTRACT

An acidic aqueous slurry composition comprising silica abrasive particles, an oxidizer, a quaternary ammonium hydroxide; and acid having a maximum pKa of about 2.5; and water is provided along with its use for polishing.

TECHNICAL FIELD

The present invention relates to an aqueous chemical formulation that isespecially useful for polishing or planarizing a surface. The presentinvention is especially useful for polishing or planarizing metals suchas those used as interconnect structures in integrated circuit devicessuch as semiconductor wafers containing copper damascene and dualdamascene feature.

BACKGROUND OF THE INVENTION

On VLSI and ULSI semiconductor chips, Al and alloys of Al are used forconventional chip interconnect/wiring material. However, more recentlycopper and alloys of copper have been developed as chip interconnectsmaterial. The use of copper and copper alloys results in improved deviceperformance when compared to Al and its alloys.

By way of example, various new memory technologies are currently underdevelopment. Particularly important are the non-volatile memory deviceswhich would allow the devices to retain the memory even after the poweris switched-off. Magnetic Random Access Memory (MRAM) is one of the mostpromising technologies in this regard. MRAM offers a great potential forhigh density, high speed and low power consumption.

MRAM devices are based on a phenomenon known as Giant Magneto Resistance(GMR). GMR is exhibited when an electric field is applied across twolayers of a ferromagnetic layers separated by a thin non-magnetic layer.The electrical conductivity across these layers depends on theorientation of the magnetic field of the two ferromagnetic layersrelative to each other. When the orientations are parallel, theelectrical conductivity is highest; and when they are anti-parallel, theconductivity is the lowest. GMR refers to this large difference in theelectrical conductivity depending on the orientation of the magneticfield.

A MRAM device employs multiple metallization layers including barrierlayers (typically Ta and/or TaN), copper, ferromagnetic layers(typically a Fe—Ni alloy) and a metal (from group 4d and 5d of theperiodic table; most commonly ruthenium, rhodium, iridium and rhenium),which exhibits inter-layer exchange coupling with the ferromagneticmaterial. The damascene process coupled with chemical mechanicalplanarization (CMP) is used to define the MRAM structures. This processwhich is in concept similar to that used with the copper interconnectformation in typical semiconductor fabrication is also used. TheDamascene process typically involves blanket depositing the metalliclayers over a layer of dielectric which has trenched features etchedinto its surface. The deposited metal fills the pre-etched gaps ortrenches in the dielectric, and leaves a metal overabundance on thesurface of the wafer which must be removed. Once the metal overabundancehas been removed, an inlaid metal wiring structure is left on thesurface of the wafer. The removal of the metal is achieved by chemicalmechanical polishing (CMP).

Use of multiple metallization layers which differ greatly in chemicaland mechanical properties pose a great challenge for chemical mechanicalplanarization. Ideally it would be desirable that a single slurry isable to remove all these layers without compromising planarity ordefectivity related to corrosion.

In the practice of chemical mechanical polishing, several criticalrequirements must be met in terms of the slurry component properties.For instance, retention of colloidal stability of the slurry componentsduring storage, after blending, and just prior to use is an importantspecification. In practice, polishing slurries are typically twocomponent systems. The abrasive component contains the abrasive, and mayalso contain organic acid(s), chelate(s), surfactant(s), corrosioninhibitor(s), and other additives. The second component is the oxidizer.The two components and typically keep separate until time of use due tothe fact that the oxidizer would react with the other components overtime, placing a limitation on the shelf life of the product. Afterblending and just prior to use, it is important that the blended slurryretains its colloidal stability and polish performance for several days.This is because after blending, the blended slurry may sit in a primarytank and be delivered to the polisher over the course of several hoursto several days. Hence the pot life of the blended slurry is a keyspecification for a commercial product.

BRIEF SUMMARY OF THE INVENTION

The present invention provides slurry compositions that are suitable forCMP. Compositions of the present invention make possible effectiveremoval of metallic layer including those used in MRAM devices asdiscussed above in a minimum number of steps while assuring goodplanarity, absence of corrosion and excellent colloidal stability forthe abrasive particles in the slurry.

The slurry compositions of the present invention comprise:

-   -   A. about 0.01% by weight to about 50% by weight of abrasive        particles;    -   B. about 0.01% to about 50% by weight of an oxidizer;    -   C. at least about 100 ppm of quaternary ammonium hydroxide;    -   D. an acid having a pKa of about 2.5 or lower in an amount        sufficient to provide an acidic pH;    -   and F. water.

A further aspect of the present invention relates to a method forpolishing or planarizing a substrate which comprises contacting thesubstrate with the above disclosed composition and polishing orplanarizing the substrate by chemical-mechanical polishing.

A still further aspect of the present invention relates to a method forfabrication semiconductor integrated circuits comprising formingcircuits on the surface of a semiconductor wafer by photolithographicand plating processes, polishing or planarizing the circuitry bycontacting the semiconductor wafer with the above disclosed compositionand polishing and planarizing the circuitry by chemical-mechanicalpolishing.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in the art from the following detaileddescription, wherein it is shown and described preferred embodiments ofthe invention, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects withoutdeparting from the invention. Accordingly, the description is to beregarded as illustrative in nature and not as restrictive.

SUMMARY OF FIGURES

The FIGURE shows electrochemical polarization of difference films.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

The compositions of the present invention contain abrasive particlessuch as silica, alumina, zirconia, titania, ceria and the like withsilica being most typical.

The abrasive particles typically have particle sizes of about 10 toabout 1000 nanometers and more typically about 10 to about 200nanometers.

The concentration of the abrasive particles is typically about 0.01% toabout 50%, more typically about 0.1% to about 20% of weight and evenmore typically about 5% to about 15% by weight.

The compositions of the present invention also contain an oxidizingagent. Suitable oxidizing agents include oxidizing metal salts,oxidizing metal complexes, nonmetallic oxidizing acids such as peracetic and periodic acids, iron salts such as nitrates, sulfates EDTA,citrates, potassium ferricyanide and the like, hydrogen peroxide,aluminum salts, sodium salts, potassium salts, ammonium salts,quaternary ammonium salts, phosphonium salts, or other cationic salts ofperoxides, chlorates, perchlorates, nitrates, permanganates, persulfatesand mixtures thereof.

The preferred oxidizing agent is hydrogen peroxide. The oxidizingagent(s) are typically present in the composition in amounts of about0.01% wt. to about 50 wt. %, more typically about 0.05 wt. % to about 5wt. % and even more typically about 0.1 wt. % to about 1 wt. %.

The compositions of the present invention also contain a quaternaryammonium hydroxide. The quaternary ammonium hydroxide improves the shelflife of the slurry by the way of increasing colloidal stability.Quaternary ammonium hydroxide bases have been found to improve thecolloidal stability of silica particles in the acidic pH environment ofthe compositions of the present invention.

The quaternary ammonium compound can be represented by the formula[NR₄R₅R₆R₇]OH wherein each of R₄, R₅, R₆ and R₇ individually is an alkylgroup.

The term “alkyl” refers to straight or branched chain unsubstantiatedhydrocarbon groups of 1 to 20 carbon atoms, preferably 1 to 8 carbonatoms. The expression “lower alkyl” refers to alkyl groups of 1 to 4carbon atoms. Examples of suitable alkyl groups include methyl, ethyl,proplyl and butyl. Typical quaternary ammonium hydroxides aretetraalkylammonium and aryltrialkylammonium hydroxides such astetramethylammonium hydroxide, tetraethylammonium hydroxide,tetrapropylammonium hydroxide, tetrabutylammonium hydroxide,ethyltrimethylammonium hydroxide, diethyldimethylammonium hydroxide andbenzyltrimethylammonium hydroxide.

Typical concentrations of quaternary ammonium hydroxide bases is about500 ppm or higher, more typically about 1000 ppm or higher and even moretypically 2500 ppm or higher with the maximum typically being about1.5%.

The compositions of the present invention also comprise at least oneacid having a pKa of 2.5 or lower and more typically about 1.5 or lower.Typical acids are inorganic acids such as phosphoric acid, nitric acid,sulfuric and hydrochloric acid; and organic carboxylic acids such asoxalic acid, malonic acid, and citric acid; with phosphoric acid beingthe most typical. The amount of acid to provide an acidic pH for theslurry, typically above about 1.5 and more typically about 2 or above,and even more typically a maximum pH of about 5. A pH of above 1.5 makesit possible to reduce corrosion related issues. In the case ofphosphoric acid, the concentration is about 0.05% to about 5% by weightand more typically about 0.1% by weight to about 1% by weight.Compositions may optionally also contain acids having pKa greater than2.5 in combination to the acids with pKa of less than 2.5.

The water is typically present in amounts of about 70% to about 95% byweight, more typically about 80% to about 90% by weight, and even moretypically about 85% by weight in the slurry.

The compositions of the present invention can optionally also include acopper corrosion inhibitor. The relative amounts of copper corrosioninhibitor, when present, is typically about 100 ppm (0.01%) to about15,000 ppm (1.5%), and more typically about 1,000 ppm (0.1%) to about10,000 ppm (1%) in the slurry. A typical corrosion inhibitor isbenzotriazole

Examples of corrosion inhibitors are aromatic hydroxyl compounds,acetylenic alcohols, carboxyl group containing organic compounds andanhydrides thereof, imidazoles and triazole compounds.

Exemplary aromatic hydroxyl compounds include phenol, cresol, xylenol,pyrocatechol, resorcinol, hydroquinone, pyrogallol, 1.2.4-benzenetriol,salicyl alcohol, p-hydroxybenzyl alcohol, o-hydroxybenzyl alcohol,p-hydroxyphenethyl alcohol, p-aminophenol, m-aminophenol, diaminophenol,amino resorcinol, p-hydroxybenzoic acid, o-hydroxybenzoic acid2,4-dihydroxybenzoic acid, 2-5-dihydroxybenzoic acid,3,4-dihydroxybenzoic acid and 3,5-dihydroxybenzoic acid.

Exemplary acetylenic alcohols include 2-butyne-1,4-diol,3,5-dimethyl-1-hexyn-3-ol, 2 methyl-3-butyn-2-ol,3-methyl-1-pentyn-3-ol, 3,6-dimethyl-4-octyn-3,6-diol,2,4-7,9-tetramethyl-5-decyne-4,7-diol and 2,5-dimethyl-3-hexyne2,5-diol.

Exemplary carboxyl group containing organic compounds and anhydridesthereof include formic acid, acetic acid, propionic acid, butyric acid,isobutyric acid, oxalic acid, malonic acid, succinic acid, glutaricacid, maleic acid, fumaric acid, benzoic acid, phthalic acid,1,2,3-benzenetricarboxylic acid, glycolic acid, lactic acid, malic acidcitric acid, acetic anhydride and salicylic acid.

Exemplary triazole compounds include benzotriazole, 1, 2, 4-triazoleo-tolyltriazole, m-tolyltriazole, p-tolyltriazole, carboxybenzotriazole,1-hydroxybenzotriazole, nitrobenzotriazole anddihydroxypropylbenzotriazole.

The compositions of the present invention also contain a surface activeagent. Suitable surface active agents include anionic, cationic,nonionic and zwitterionic compounds. Examples of some surfactants foruse in the present invention are disclosed in, for example, Kirk-Othmer,Encyclopedia of Chemical Terminology, 3rd Edition, Vol. 22 (John Wiley &Sons, 1983), Sislet & Wood, Encyclopedia of Surface Active Agents(Chemical Publishing Co., Inc. 1964), McCutcheon's Emulsifiers &Detergents, North American and International Edition (McCutcheonDivision, The MC Publishing Co., 1991), Ash, The Condensed Encyclopediaof Surfactants (chemical Publishing Co., Inc., 1989), Ash, What EveryChemical Technologist Wants to Know About . . . Emulsifiers and WettingAgents, Vol. 1 (Chemical Publishing Co., Inc., 1988), Tadros,Surfactants (Academic Press, 1984), Napper, Polymeric Stabilization ofColloidal Dispersion (Academic Press, 1983) and Rosen, Surfactants &Interfacial Phenomena, 2^(nd) Edition (John Wiley & sons, 1989), all ofwhich are incorporated herein by reference.

Typical examples of suitable surface active agents are: Na-alkylsulfates, Na-alkyl sulfonates, quarternary such as tetramethyl ammoniumhalides, Cetyl trimethy ammonium halides, hydroxides, nonyl ethers andcombinations thereof. Preferred surface active agents are sulfates suchas Na-hexyl, -heptyl, -octyl, nonyl and -lauryl sulfates with Na octylsulfate being most preferred. Na octyl sulfate is commercially availableunder its trade designation of Dupanol 80 (Witco)), StandapolLF(Henkel/Cognis), Texapon 842, (Henkel), Texapon 890 (Henkel) SulfotexOA (Henkel) and Polystep B-29 (Stephan).

The amount of surface active agent is typically about 0.1 to about 100ml/l and more typically about 20 to about 50 ml/l.

A further feature of the present invention is that the composition evenin concentrated form is relatively stable. For instance, concentrates ofthe composition can be provided and transported to the end user, theuser can then dilute it such as about a 5:1 dilution and more typicallyabout a 3:1 dilution by weight at the process tool for convenience andfor economical reasons.

The structures treated pursuant to the present invention are typicallysemiconductor devices having copper interconnects (lines, plugs, vias,global and local interconnects) embedded into a dielectric material suchas silicon dioxide, which may also include a capping layer, such assilicon nitride as in low k dielectric/damascene and dual damascenestructures. The silicon dioxide is typically a high density plasmadeposited silicon dioxide or TEOS (tetraethylorthosilicate).

The copper interconnects typically use either tantalum, tantalumnitride, or titanium or titanium nitride as a barrier or liner materialbetween the copper and the dielectric as discussed above, the presentinvention finds special suitability in fabricating non-volatile memorydevices.

Accordingly the present invention is suitable for polishing asemiconductor substrate comprising of (i) a ferromagnetic metal layer(ii) a metal from group 3d or 5d of the periodic table (for exampleruthenium, iridium, palladium, platinum, etc.) (iii) a conducting metal(such as copper, aluminum) (iv) an associated barrier layer (forexample, tantalum, tantalum nitride, titanium, titanium nitride cobaltbased barrier layers and/or tungsten based barrier layers) and (iv) anassociated dielectric layer (such as silicon dioxide). Examples of suchapplications include but not restricted to manufacturing of capacitorswhich have relatively high dielectric constants, formation of copperdamascene interconnects (with or without involving the noble metals orthe ferromagnetic materials), and processing of hard disk drives.

As such, the CMP composition contacts a variety of different materials,copper, the dielectric or capping layer, as well as the wafer backside,which is generally a thin layer of oxidized silicon as a minimum.Accordingly, the polishing composition must be selective to remove themetal as contracted to the dielectric.

The parameters of the polishing or planarizing can be determined bythose skilled in the art once aware of this disclosure, withoutexercising undue experimentation. For instance, the rate of rotation ofthe polishing platen (pads) is about 20 to about 100 rpm, and the speedof the rotation of the wafer carrier is about 20 to about 100 rpm andthe down force about 2 to about 10 psi. The polishing pads are thoseconventionally used in polishing for microelectronics.

The following non-limiting examples are presented to further illustratethe present invention:

EXAMPLE 1

The following composition is made by missing the following components inthe concentrations listed bellowed. The pH of the slurry is 2.5:Concentrations in ppm PoliEdge 2001 silica 128571 Benzotriazole 6500Tetrabutyl ammonium hydroxide 4000 Phosphoric acid 4488 Deionized waterBalance

To this slurry, hydrogen peroxide is added as an oxidizer to oxidize themetallic layers to be polished. Dilution for polishing is 70 parts byvolume of slurry: 29 parts by volume of deionized water: 1 part byvolume of 30% hydrogen peroxide.

Polishing is performed on a IPEC 472 CMP tool. The polishing parametersare:

-   -   Pressure: 3 psi    -   Platen Speed: 90 RPM    -   Carrier Speed: 30 RPM    -   Back-pressure: 2 psi    -   Slurry Flow rate: 200 ml/min    -   Polish Pad: k-grooved IC 1000    -   Polish time: 60 seconds

The removal rates of the metal films are calculated based on the changesin thickness upon polishing as measured by sheet resistance measurementtechnique with Prometrix RS35 tool. For the TEOS film thickness ismeasured by Philips SD200 ellipsometer.

The following table summarizes the removal rate data for various filmson wafers with 8″ diameter. Film Removal Rate (RR) (A/min) Cu 304 Ta1024 TEOS 1230 FeNl 2008 Ru 251

The data shows that the removal rates are high enough for a goodindustrial throughput.

EXAMPLE 2

A 8″ patterned wafer containing 9000A deep trenches patterned inside aTEOS dielectric. The trenches are filled with a metallization stackconsisting of 200 A Ta/100A Ru/250A NiFe/100A Ru/9000A Cu. The copperfilm deposited on the regions outside the trenches is first removedusing a copper CMP process using a slurry with Cu:Ta removal rateselectivity of more than 100. This results in a wafer with copperrestricted to the trenches. The remaining wafer is still covered withthe Ta/Ru/NiFe/Ru metallization layer. The slurry described in example 1along with the hydrogen peroxide dilution also described in example 1 isused to remove these metallic layers. CMP polish parameters except forthe polish time are identical as in example 1.

The following table tabulates the dishing topography for 100 micronlines for wafers polished at different stages. This topography ismeasured using VEECO AFP. After the initial 45 seconds, the wafer ismostly free from all the metallic layers from the regions outside thetrenches. A subsequent 45 seconds of over polish results in correctionof initial high topography. This results in a very planar surface withlow topography. 45 second polish 90 second polish After copper CMP usingslurry in using slurry in step Example 1 Example 1 Center Die 1625 1994176 Mid-Die 1716 1940 294 Edge Die 2408 2397 786

Visual and microscopic examination of the polished wafers shows nocorrosion defects.

EXAMPLE 3

Electrochemical polarization characteristics of different film types inthe slurry described in example 1 and diluted with hydrogen peroxide asshown in example 1 are measured using EG&G M263potentiostate/galvanostat controlled by SofetcorrII corrosion software.The Scan rate is 0.25 mV/s. FIG. 1 show the Electrochemical polarizationcurves.

The electrochemical polarization curves in the FIGURE show that thecopper corrosion potential in the slurry mixed diluted as described inexample 1 is anodic with respect to ruthenium and Fe—Ni alloy. So incase of a galvanic coupling formed between copper and any of thesematerials, copper will be thermodynamically favored to be protected.This would result in superior corrosion protection for copperlines/structures.

EXAMPLE 4

Slurry samples are prepared containing 2500 ppm phosphoric acid, 500 ppmnitric acid, 10% Poliedge 2001 silica and a base to bring the pH up-to2. Different bases used for the slurry formulations are listed in tablebelow. The samples are aged in an oven at 50° C. for 7 days. From thetable it is apparent that the quaternary ammonium hydroxides such astetrabutyl ammonium hydroxide and tetramethyl ammonium hydroxide areuseful in improving the colloidal stability of the slurries in acidicpH. Base pH 7 days at 50° C. Ammonia 1.99 88.4 KOH 1.97 88.5 No base1.53 84.1 TBAH 1.99 75 TMAH 1.99 77.5

EXAMPLE 5

The following compositions are fabricated: Composition (ppm) (grams)PoliEdge 2001 Benzo- Phosphoric Nitric Example 1 Silica triazole TBAHAcid Acid pH 6A 128571 5000 6480 500 2500 2.54 6B 128571 1000 6091 5002500 2.48

The balance of the above compositions is water.

These slurries are diluted with 30% hydrogen peroxide and water in thevolume ratio 70 parts slurry: 29 parts water: 1 part of 30% hydrogenperoxide. Cu, Ta, TEOS, Ru and Re—Ni films on 8″ wafer substrates arepolished using the protocol described in Example. The following tablesummarizes the removal rate data. EXAMPLE 6A 6B Cu 418 355 Ta 1161 1005TEOS 1139 1094 Ru 542 744 FeNl 1108 770

EXAMPLE 6

The slurry described in Example 1 is mixed with de-ionized water and 30%hydrogen peroxide in different ratios. These formulations aresubsequently used to polish copper films with 6″ diameter. The polishingprotocol is the same as described in Example 1.

As seen from this example, the copper removal rates can be tuned towhatever desired level by simply changing hydrogen peroxide amount addedat the time of polishing. High copper removal rates are possible usingthis method which can potentially allow only compositions having thesame components but differing in the relative concentration of theoxidizing agent to be used for entire polishing operation includingcopper overburden removal step and the barrier/sandwich removal layerstep. If a tighter control of topography is needed, the same slurry canbe used at two different concentrations during these stages. In copperoverburden removal, peroxide concentration may be maintained high toallow high copper rates and thus high throughput. As the copperoverburden is cleared, peroxide concentration may be reduced to reducecopper removal rates and thus making it possible to have a low finaltopography.

The foregoing description of the invention illustrates and describes thepresent invention. Additionally, the disclosure shows and describes onlythe preferred embodiments of the invention but, as mentioned above, itis to be understood that the invention is capable of use in variousother combinations, modifications, and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein commensurate with the above teachings and/or the skillor knowledge of the relevant art. The embodiments described hereinaboveare further intended to explain best modes known of practicing theinvention and to enable others skilled in the art to utilize theinvention in such, or other, embodiments and with the variousmodifications required by the particular applications or uses of theinvention. Accordingly, the description is not intended to limit theinvention to the form disclosed herein. Also, it is intended that theappended claims be construed to include alternative embodiments. Allpublications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference.

1. An aqueous slurry composition which comprises: A. about 0.01% byweight to about 50% by weight of abrasive particles; B. about 0.01% toabout 50% by weight of an oxidizer; C. at least about 500 ppm of aquaternary ammonium hydroxide; D. an acid having a pKa of about 2.5 orlower in an sufficient amount to provide an acidic pH; and E. water. 2.The composition of claim 1 wherein the amount of the abrasive particlesis about 1% to about 20% by weight.
 3. The composition of claim 1wherein the amount of the abrasive particles is about 5% to about 15% byweight.
 4. The composition of claim 1 wherein the abrasive particlescomprises silica particles.
 5. The composition of claim 1 wherein theoxidizer comprises hydrogen peroxide.
 6. The composition of claim 1wherein the amount of oxidizer is about 0.05 at % to about 5 wt %. 7.The composition of claim 1 wherein the amount of oxidizer is about 0.1wt, % to about 1 wt. %.
 8. The composition of claim 1 wherein thequaternary ammonium hydroxide is represented by the formula:[NR₄R₅R₆R₇]⁻OH wherein each of R₄, R₅R₆ and R₇ individually is an alkylgroup of 1 to 20 carbon atoms.
 9. The composition of claim 8 wherein thealkyl group contains 1 to 4 carbon atoms.
 10. The composition of claim 1wherein the quaternary ammonium hydroxide comprises tetramethyl ammoniumhydroxide or tetrabutyl ammonium hydroxide.
 11. The composition of claim1 wherein the amount of quaternary ammonium hydroxide is about 1000 ppmor higher.
 12. The composition of claim 1 wherein the amount ofquaternary ammonium hydroxide is about 2500 ppm or higher.
 13. Thecomposition of claim 1 wherein the acid comprises phosphoric acid. 14.The composition of claim 1 wherein the pH is at least about 1.5.
 15. Thecomposition of claim 1 wherein the pH is about 1.5 to about
 5. 16. Thecomposition of claim 1 wherein the pH is at least about
 2. 17. Thecomposition of claim 1 which further comprises a corrosion inhibitor.18. The composition of claim 16 wherein the corrosion inhibitorcomprises benzotriazole.
 19. The composition of claim 1 which furthercomprises a surface active agent.
 20. A method for polishing a metalwhich comprises providing on the metal an aqueous slurry compositioncomprising: A. about 0.1% by weight to about 50% by weight of abrasiveparticles; B. about 0.1% to about 50% by weight of an oxidizer; C. atleast about 500 ppm of a quaternary ammonium hydroxide; D. an acid beinga pKa of about 2.5 or lower in amount to provide an acidic pH; and E.water; and contacting the metal with a polishing pad.
 21. A process forfabricating semiconductor integrated circuit structure comprising:forming circuits on the surface of a semiconductor wafer byphotolithographic process; planarizing the surface by chemicalmechanical polishing with the composition of claim
 1. 22. The process ofclaim 21 wherein the integrated circuit structure comprise asemiconductor substrate; a ferromagnetic metal layer; a metal selectedfrom the group consisting of group 3d and 5d of the periodic table; alayer of copper or aluminum; a barrier layer; and a dielectric layer.